1. Field of Invention
The present invention relates to a composite optical film applicable to a liquid crystal display.
2. Description of Related Art
Generally, a structure of a liquid crystal display (LCD) mainly includes a panel and a backlight module. The backlight module serving as a light source of the liquid crystal display includes a spot light source (e.g. a light-emitting diode) or a linear light source (e.g. a fluorescent lamp), a light guide plate and various optical films. Among the various elements of the backlight module, the spot light source or the linear light source consumes the most power and generates the biggest amount of heat. Therefore, it is an important subject how to reduce the power consumption and the heat-generating amount of the spot light source or the linear light source while maintaining or even enhancing brightness of the liquid crystal display.
At present, various optical films are used in the backlight module to efficiently make use of the light source, thereby enhancing the brightness of the LCD panel. This does not need to change the design of any element or consume additional power, so it has become the most economic and easy solution, for example, by use of a light-gathering film. The light-gathering film is always called the brightness enhancement film or prism film in this field. The light-gathering film mainly functions to gather the scattered light based on refraction and internal total reflection and then emit the light in the on-axis direction of about ±35°, so as to enhance the brightness of LCD. However, the light-gathering film typically has regularly-arranged light-gathering micro structures, which causes an interference or diffraction phenomenon of light refracted or reflected by different optical elements, so the liquid crystal display presents rainbow grain, light and shade stripes, moiré or Newton's ring.
To solve the above problems, a common method adopted in this field is to add a protective diffuser (or referred to as a top diffuser) to alleviate the above optical phenomenon. However, the disadvantages are that the top is diffuser costs too much and the thickness of the backlight module is increased after the optical film is added, and thus the backlight module becomes complicated, which does not conform to the trend of light and thin.